1. Field of the Invention
The present invention relates to a motor control apparatus, and more particularly, to a motor control apparatus that detects the current of a motor and feeds back the detected motor current, thereby subjecting the motor to current feedback control.
2. Description of the Prior Art
In a generally known motor control method, the driving current of a motor is detected, and the motor is feedback-controlled so that the detected motor current value is equal to a command current value. In subjecting an inverter unit to PWM control to carry out current control, for example, driving currents for individual phases of the motor are detected, and PWM signals are originated so that the detected motor current values are equal to command current values for the individual phases. Based on the originated PWM signals, the inverter unit is regulated to control the motor currents for the individual phases.
In this motor control apparatus, a resistor is inserted in series in an electric conductor or output wire of the inverter unit through which the motor currents flow, and a potential difference across the resistor is detected, whereby the motor driving currents are detected. Described in Japanese Patent Application Laid-Open No. 7-15972 is a method in which detected motor currents are ΔΣ—modulated so that they can be fed back accurately.
If a resistor for current detection is inserted in a circuit through which a current to drive the motor flows, in order to detect the actual current of the motor, it generates heat. If a high motor driving current is run, in particular, heat release from the resistor is substantial, so that the capacity of the resistor must be increased. Further, this heat release worsens the environment of installation of the motor and the motor control apparatus, e.g., the inverter unit, and exerts a bad influence upon peripheral apparatuses. If an attempt is made to feed back accurate driving currents by ΔΣ modulation by means of a ΔΣ modulator circuit, therefore, the effect of the ΔΣ modulation is reduced by half.